Cephalexin vs. Amoxicillin

  • Medical Editor: John P. Cunha, DO, FACOEP
    John P. Cunha, DO, FACOEP

    John P. Cunha, DO, FACOEP

    John P. Cunha, DO, is a U.S. board-certified Emergency Medicine Physician. Dr. Cunha's educational background includes a BS in Biology from Rutgers, the State University of New Jersey, and a DO from the Kansas City University of Medicine and Biosciences in Kansas City, MO. He completed residency training in Emergency Medicine at Newark Beth Israel Medical Center in Newark, New Jersey.

What's the Difference Between Cephalexin and Amoxicillin?

What Are Cephalexin and Amoxicillin?

Cephalexin belongs to a class of antibiotics called cephalosporins. They are similar to penicillin in action and side effects. They stop or slow the growth of bacterial cells by preventing bacteria from forming the cell wall that surrounds each cell. The cell wall protects bacteria from the external environment and keeps the contents of the cell together, and without a cell wall, bacteria are not able to survive. Bacteria that are susceptible to cephalexin include Staphylococcus aureus, Streptococcus pneumoniae, Haemophilus influenzae, E. coli and several others. Cephalexin is used for treating genital and urinary tract infections, bone infections, ear infections, skin and skin structure infections, respiratory infections, pharyngitis, mastitis, and bladder infections.

Amoxicillin belongs to a class of antibiotics called penicillins. Other members of this class include ampicillin (Unasyn), piperacillin (Pipracil), ticarcillin (Ticar), and others. These antibiotics all have a similar mechanism of action. They do not directly kill bacteria, but they stop bacteria from multiplying by preventing bacteria from forming the walls that surround them. Amoxicillin is effective against many different bacteria including H. influenzae, N. gonorrhoea, E. coli, Pneumococci, Streptococci, and certain strains of Staphylococci.

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What Are the Side Effects of Cephalexin and Amoxicillin?

Cephalexin

The most common side effects of cephalexin are:

Individuals who are allergic to penicillin may also be allergic to cephalexin. Serious but rare reactions include seizures, severe allergic reactions (anaphylaxis), and low platelet or red blood cell count.

Cephalexin, like almost all antibiotics, may cause mild or severe cases of pseudomembranous colitis, a mild to severe inflammation of the colon. Antibiotics, including cephalexin alter the types of bacteria in the colon and permit overgrowth of a bacterium called Clostridium difficile. Studies indicate that toxins produced by Clostridium difficile are a primary cause of pseudomembranous colitis.

Amoxicillin

Side effects due to amoxicillin include:

People who are allergic to the cephalosporin class of antibiotics, which are related to the penicillins, for example, cefaclor (Ceclor), cephalexin (Keflex), and cefprozil (Cefzil), may or may not be allergic to penicillins.

Serious but rare reactions include:

Amoxicillin can alter the normal bacteria in the colon and encourage overgrowth of some bacteria such as Clostridium difficile which causes inflammation of the colon (pseudomembranous colitis). Patients who develop signs of pseudomembranous colitis after starting amoxicillin (diarrhea, fever, abdominal pain, and possibly shock) should contact their physician immediately.

What Is the Dosage for Cephalexin vs. Amoxicillin?

Cephalexin

The dose of cephalexin for adults is 1 to 4 grams in divided doses. The usual adult dose is 250 mg every 6 hours. Some infections may be treated with 500 mg every 12 hours. Children are treated with 25-100 mg/kg/day in divided doses. The dosing interval may be every 6 or 12 hours depending on the type and seriousness of the infection.

Amoxicillin

  • For most infections in adults the dose of amoxicillin is 250 mg every 8 hours, 500 mg every 8 hours, 500 mg every 12 hours or 875 mg every 12 hours, depending on the type and severity of infection.
  • For the treatment of adults with gonorrhea, the dose is 3 g given as one dose.
  • For most infections, children older than 3 months but less than 40 kg are treated with 25 or 45 mg/kg/day in divided doses every 12 hours or 20 or 40 mg/kg/day with one-third of the daily dose given every 8 hours depending on the type and severity of the infection.
  • Amoxicillin can be taken with or without food.

What Drugs Interact with Cephalexin and Amoxicillin?

Cephalexin

Cephalexin may reduce the effect of BCG and typhoid vaccines. Cephalexin should not be combined with BCG or typhoid vaccine unless there are no other options.

Amoxicillin

Amoxicillin is rarely associated with important drug interactions.

Are Cephalexin and Amoxicillin Safe to Use While Pregnant or Breastfeeding?

Cephalexin

Amoxicillin

  • Penicillins are generally considered safe for use by pregnant women who are not allergic to penicillin.
  • Small amounts of amoxicillin may be excreted in breast milk and may cause diarrhea or allergic responses in nursing infants. Amoxicillin is generally considered safe to use while breastfeeding. Amoxicillin is used to treat infections in the newborn.

Summary

Cephalexin (Keflex, Daxbia) belongs to a class of antibiotics called cephalosporins. They are similar to penicillins -- the class to which amoxicillin (Moxatag) belongs -- in action and side effects. Both are used to treat various bacterial infections.

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Medically Reviewed on 2/16/2018
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